High-purity oxytocin is a peptide hormone secreted by the posterior pituitary gland. Synthesized within the paraventricular and supraoptic nuclei of the hypothalamus, it consists of nine amino acids and is transported to the neurohypophysis for release at a rate of 2 to 3 millimeters per day. The cysteine (Cys) residues located at positions 1 and 6 form a cyclic hexapeptide structure via a disulfide bond.
The chemical structure of oxytocin in humans and most mammals is as follows:
Cysteine-Tyrosine-Isoleucine-Glutamine-Aspartic Acid-Cysteine-Proline-Leucine-Glycine-NH2
The structure of oxytocin is highly similar to that of antidiuretic hormone (Cysteine-Tyrosine-Phenylalanine-Glutamine-Aspartic Acid-Cysteine-Proline-Arginine-Glycine-NH2).